Thousands of people gathered on the Japanese island of Okinawa on Sunday in one of the biggest demonstrations in two decades against U.S. military bases following the arrest of an American suspected of murdering a local woman.

The protest marks a new low for the United States and Japanese Prime Minister Shinzo Abe in their relations with the island and threatens plans to have the U.S. Marines Futenma air station moved to a less populous part of the island.

The United States and Japan agreed in 1996 to close the Futenma site, located in a residential urban area, after the rape of a 12-year-old Japanese schoolgirl by three U.S. military personnel spurred mass demonstrations against the American presence.

That plan has been on hold since residents living near the proposed relocation site protested against the move, worried about noise, pollution and crime.

Okinawa assembly members opposed to the move won a majority in the prefectural assembly election this month, providing renewed support for Okinawa Governor Takeshi Onaga's plan to have the base move elsewhere.

Okinawa hosts 50,000 U.S. nationals, including 30,000 military personnel and civilians employed at U.S. bases.

The site of some of the bloodiest fighting between U.S. and Japanese forces in World War Two, Okinawa remained under American occupation until 1972 and around a fifth of its land is still under U.S. military control.

Yet, with the United States and Japan looking to contain China's growing might in the East China Sea, the Okinawan island chain, which stretches close to Taiwan, is becoming strategically more valuable to military planners.

Japan's Self Defense Force, which is pivoting away from defending its northern borders from a diminished Russian threat, is fortifying the region with radar bases and anti-ship missile batteries.

Last month's arrest of the 32-year-old U.S. civilian working at a U.S. base prompted the U.S. military to announce a 30-day period of mourning for the victim and restrict off-base drinking on the island in a bid to assuage local anger.

But relations were further frayed by the subsequent arrest of a U.S. sailor on Okinawa on suspicion of drunk driving following a car crash.